Development of a coherent gradient-sensing tomographic interferometer for three-dimensional refractive index-based measurements

Non-invasive measurement of thermophysical properties such as temperature, density or concentration in a fluid medium remains a very challenging problem. Laser interferometry is one of many optical techniques employed for non-invasive measurement of refractive index field and can be used to provide information on the thermophysical properties in a convective fluid system. In conjunction with tomography, laser interferometry allows for a convenient full-field measurement in three dimensions. In the present paper, a novel interferometric technique known as coherent gradient-sensing (CGS) interferometry is combined with tomography to develop a powerful new tool for time-dependent three-dimensional (3-D) refractive index-based measurements in fluid-thermal systems. The paper discusses the design and layout of the instrument, which is currently under development, some preliminary results, and the necessary data reduction techniques to be employed. An error estimation of the instrument is also presented.